Solidification microstructure selection and characteristics in the Zn-based ZnAl system

Abstract

A solidification microstructure selection diagram has been determined for ZnAl alloys containing 2–10 wt% Al by Bridgman and TIG weld traversing over the growth velocity range 0.01–21 mm/s. Secondary dendrite arm spacings λ 2 of αZn and βAl decreased with increasing V such that λ 2V 1 3 is constant at fixed alloy concentration. Eutectic cell size Λ decreased with increasing V such that ΛV 1 2 is constant at 690 ± 130 μ m 3 2 s −1 2 . Eutectic interphase spacing λ decreased with increasing V such that λV 1 2 is constant at 7.1 ± 0.8 μ m 3 2 s −1 2 over the growth velocity range 0.01–21 mm/s in excellent agreement with predictions of the Jackson-Hunt model. Hardness of the eutectic exhibited a Hall-Petch relationship with eutectic interphase spacing λ and eutectic cell size Λ. The value of k y from the eutectic interphase spacing is intermediate in value between those for grain size hardening of the pure constituents.